1. Field of the Invention
The field of the present invention is a valve operating system for an internal combustion engine wherein the valve operating cam is operatively connected to a cam-side p and a valve-side piston is operatively connected to the engine with a hydraulic pressure chamber provided between the piston and the valve-side piston, and further a hydraulic pressure releasing valve is connected to the hydraulic pres chamber for selectively controlling the operation of the engine valve.
2. Description of the Prior Art
Such valve operating systems are conventionally known, for example, from Japanese Patent Application Laid-Open No. 275516/86. In such a system, the time of actually closing the engine valve can be shifted from the valve closing time defined in accordance with the shape of the valve operating cam by controlling the time of releasing the hydraulic pressure in the hydraulic pressure chamber through a hydraulic pressure releasing valve, thereby providing an engine valve operation mode meeting the operational condition of the engine.
In such valve operating systems, when jumping of the engine valve occurs, a working oil, in response to an increase in the volume of the hydraulic pressure chamber between the valve-side piston and the cam-side piston, is supplied in an amount corresponding to such increase in volume from a pressure oil supply source to the hydraulic pressure chamber. Therefore, if the engine valve is operated in accordance with the shape of the valve operating cam without releasing the hydraulic pressure in the hydraulic pressure chamber, the engine valve remains open or lifted in an amount corresponding to the amount of extra working oil supplied in the above manner, when the cam-side piston engages the base circle portion of the valve operating cam. Thus, complete seating or closing of the engine valve is difficult.
In addition, if the same working oil remains within the hydraulic pressure chamber for a long period of time, the temperature of the working oil is increased, which may cause deterioration of the properties of the working oil.